Rivals of iPad say this is the year. Again.

Welcome to the year of the tablet. Again.

Last year was supposed to be the year manufacturers would wow consumers with offerings of all sorts of tablet computers. Steven A. Ballmer, Microsoft's chief executive, took the stage in January at the International Consumer Electronics Show, the industry's premier trade show, and displayed three devices that he said would be on sale in the months ahead. Dozens of smaller companies laid out their own tablet plans at the show.

But few of these promises came to fruition; none of Microsoft's tablets ever showed up in stores.

Instead, in April, Apple's iPad came out. And the year became the Year of the iPad.

This year, manufacturers are promising it will be different, saying that after the success of the iPad, they have learned a lot about what consumers want in a tablet.

"We could have done this a year ago and rushed it out, but it wouldn't have had the right features," said Phil Osako, director of product marketing at Toshiba, which is introducing a new tablet at this year's show, which begins Thursday in Las Vegas.

Perhaps the most important feature is the ability to watch high-quality video, say industry analysts, pointing to market research showing that, above all, consumers want to use tablets for all kinds of media consumption -- watching films, looking at and sharing photographs, playing games.

"Apple competitors' first instinct was to build a cheaper device and put a cheaper processor in it," said Sarah Rotman Epps, an analyst with Forrester Research, a market research firm. "The problem with that is that it wouldn't have been as good for the video screens."

At this year's show, Research In Motion and Hewlett-Packard are expected to show off tablet computers, while scheduled appearances by executives at Motorola and Microsoft are widely thought to be coming-out parties for their company's devices.

Mr. Ballmer is to give the keynote address in Las Vegas on Wednesday, the eve of the show; some analysts and bloggers have described this as a do-over of last year.

And on the show floor this year, manufacturers whose primary expertise rests in cellular phones, personal computers and even televisions are planning to display their first forays into the tablet market.

At the same time, industry analysts say demand for these devices is poised to spike. More than 24 million tablet computers are projected to be sold in the United States this year, up from 10.3 million in 2010, according to Forrester. IDC, another research firm, expects to see 42 million tablet sales worldwide in 2011.

As of October, Apple had sold 7.46 million iPads worldwide, according to the company's last reported figures. It had virtually no competitors all year, until the Samsung Galaxy Tab became available in November. Samsung says it has sold 1.5 million Galaxy Tabs since then.

How do the competitors catch up?

Many companies are withholding the specifics of their tablets until they are formally introduced. But those who have discussed their plans say they will both offer specific features that the iPad is lacking, and undercut their competitors on price.

Mr. Osako from Toshiba said Apple's experience over the last year has helped his company by creating demand for tablets while Toshiba fine-tuned its plans. Toshiba's tablet, which will run on Google's Android operating system, resembles an iPad with a grippy rubberized backing. The company has incorporated features it has developed for its laptops, like stereo speakers and a screen that adjusts in contrast depending on the lighting. Both of those features will make it more comfortable for consumers to watch video.

Mr. Osako also listed features unavailable on the iPad, like front- and back-facing cameras, ports for H.D.M.I. hookups and SIM cards, and the ability to run Adobe Flash.

"We really view this as the next revolution," he said.

Other companies are looking to distinguish themselves by price. Enspert, a Korean manufacturer that is already selling tablets in Korea, is planning to introduce an Android tablet with a seven-inch screen for under $350 at the show, and sell it in the United States this year. By the end of the summer, the tablet, the Identity Tab, will also be available with a data plan through a major wireless carrier for about $100, Bobby Cha, the company's chief marketing officer, said in a telephone interview.

Mr. Cha said technology consumers pay a heavy premium for familiar brand names, creating opportunity for little-known companies with similar products.

"The market is open to everybody, so we know where everybody stands," he said. "Apple changed the market dynamics, but we're going to occupy a price point that is much more appealing to the American mass-market customer."

Creating similar products for much lower prices may be difficult because the iPad has conditioned customers to expect a device that is both relatively light and powerful enough to display high-quality media, said Mark Donovan, an analyst with comScore, a market research organization. But he also said that success would be determined largely based on the software that the devices run, and not only on the number of features that manufacturers can pack into the hardware.

The tablet market is shaping up to resemble the smartphone market, in which a few companies, like Apple, Research In Motion and Microsoft, design their own operating systems, while many others design hardware that runs on Google's Android operating system.

Perhaps the companies best positioned to succeed are those that make cellphones, several analysts who follow the market said. Handset makers already have relationships with wireless carriers, which can hide the full price of devices by subsidizing them when consumers also purchase data plans.

Many manufacturers are focusing solely on creating hardware that will run on Google's Android operating system. In part, companies were delayed last year because they were waiting for updated versions of Android that would be designed specifically for tablet computers. That wait seems to be over.

Devices can already run Android 2.3, known as Gingerbread, and Android 3.0, known as Honeycomb, is scheduled to be available this year. Andy Rubin, vice president for engineering at Google, showed a prototype of a Motorola tablet running the operating system at a conference in December.

Apple's experience with the iPad has also shown that consumers place a high value on the number and quality of apps. And so no matter how good tablets look in Las Vegas at the electronics show, the competition will continue as developers begin to write apps for the various devices.

"You can build these devices, which is great, but it's no longer enough to say, 'O.K., you have the Internet,' " said Mr. Donovan of comScore. "You need developers."